some thought, ignoring some of the 80s and craziness on display here:
-people absolutely can recover from headbutts. They're usually a small motion in a tight place. There were a few headbutts in the early UFC that were pretty much ignored by the fighters.

-the way he cocks back his head before assaulting that melon is pretty much not how you want to start a headbutt. If someone rocks back like that at me they're getting hit or shoved in their compromised position, or they're gonna end up crashing their face on my hairline when their cue makes me tuck my chin.

-what's with all the fruit destruction? I never assumed he couldn't destroy fruit with windup haymaker atttacks with different body weapons.

some thought, ignoring some of the 80s and craziness on display here:
-people absolutely can recover from headbutts. They're usually a small motion in a tight place. There were a few headbutts in the early UFC that were pretty much ignored by the fighters.

-the way he cocks back his head before assaulting that melon is pretty much not how you want to start a headbutt. If someone rocks back like that at me they're getting hit or shoved in their compromised position, or they're gonna end up crashing their face on my hairline when their cue makes me tuck my chin.

There were also a few kicks and punches in the early UFC that were ignored by the fighters. Here's a headbutt KO (from clinch with little windup):

Yes, headbutts can certainly end fights. I recall an old NHB fight ending when a guy in top mount pinned down the other guy's hands and headbutted his way to victory. My objection is how Vunak emphasizes, complete with dramatic pauses and intense glares, that a headbutt is something you don't recover from etc etc. It doesn't always end fights. Hell, I'd say it usually doesn't work like an off switch unless done without warning before a fight starts.

I like headbutts, but I understand that they're not a magic tool compared to other striking tools.